The surface of the earth is covered with water at 70% or more thereof. Therefore, our life is closely related to underwater environment. To comprehend problems relating to energy resources, mineral resources capable of being used and environment pollution, it is important to perform investigation at a sea bed, a lake bed, and a river bed.
It has been required in many fields to analyze the chemical composition of water and solid material in water. Currently, a sample is taken from an investigation area and chemical analysis of the sample is performed on land. However, such method is time-consuming and costly and analysis results cannot be obtained in real time. Further, there may be a risk that impurities are mixed to a sample when the sample is taken out of water onto land.
Considering the above, it is required to perform investigation in water. However, such investigation in water is associated with difficulties for the following reasons.
[Difficulty 1]
Since water pressure is high in deepwater environment, water-resistant and pressure-resistant properties are required. Further, owing to high water pressure, physical conditions in deepwater environment is different from that on land. Accordingly, there arises a case that a measurement method and device specifications in deepwater environment are required to be varied from those on land.
[Difficulty 2]
Since areas where people can directly perform investigation are limited in water, it is required in many cases to perform investigation using a submersible. Here, it is required that operations of devices and equipment and collection of information can be performed with remote control or direct robot action.
[Difficulty 3]
Since radio waves cannot travel far in underwater environment such as at a sea bed, cables or sound waves are to be adopted as communication tools. Accordingly, it is required that operations, measurement, and data collection can be performed within an investigation device in a self-sustaining manner to some extent.
Conventionally, in general, chemical analysis of a sample has been performed on land using a mass analyzer and the like after water, deposition substances or rocks in water and the like are taken as the sample. On land, since chemical analysis with high accuracy such as inductively coupled plasma (IPC) emission spectroscopic analysis and mass analysis can be performed, chemical analysis of a sample can be performed in detail.
However, to take a sample onto land, an area for investigation is limited. Further, it is time-consuming and costly. In addition, since the chemical composition of a sample are unknown at the time when the sample is taken, information feedback thereof cannot be provided to an investigation plan. Therefore, it is difficult to effectively perform investigation. Furthermore, there may be a risk that impurities are mixed to a sample when the sample is taken onto land.
In view of the above, as an analysis technology substituting as the sampling method, there has been proposed a device capable of performing on-site measurement of a multi-element analysis of chemicals contained in liquid such as water and in solid material in liquid using a method of laser induced breakdown spectroscopy (LIBS).
Chemical analysis using the LIBS has advantages described below. As being based on emission spectroscopic analysis, it is possible to simultaneously detect a plurality of elements. Further, since liquid and solid material can be directly analyzed, pretreatment of a sample is not required to be performed. Further, analysis measurement equipment can be compactified. Thus, a great advantage of the LIBS is that chemical analysis can be performed on site even for investigation in water. However, in underwater environment being at a sea bed, a lake bed, or a river bed, there have been a number of problems of being incapable of measuring unless factors of the difficulties in underwater investigation are overcome.
FIG. 1 illustrates a conventionally typical LIBS analysis device (devise based on Non-Patent Document 1 described below).
A laser beam emitted from a pulse laser 1 (with a beam emission time of the pulse laser being about 10 nsec) passes through a half mirror 7, is collected by a collecting lens 8, and passes through a window 9. Thus, a sample 10 is irradiated with the laser beam and plasma emission occurs at the sample 10. The emission light passes through the window 9 and is approximately collimated by the collecting lens 8. Then, a part thereof is reflected by the half mirror 7 and enters to a spectroscope 4 after being collected by an incident lens 11. Spectral resolution is performed at the spectroscope 4 and the spectral-resolved light enters to an ICCD camera 5 that is attached to the spectroscope 4. A computer 6 reads out a signal from the ICCD camera 5 to obtain spectral information associated with plasma emission at the sample 10.
In this specification, spectral information obtained by a LIBS analysis device (chemical analysis device) as being associated with plasma emission due to irradiation to a sample with laser light is called a LIBS signal.
Since the emission time of the pulse laser is extremely short, normally, the computer 6 reads out a signal from the ICCD camera 5 with a delay time after a timing signal generator 3 outputs an ON signal of a Q-switch to the pulse laser 1.